In the case of high-power rotating electrical machines, the associated windings are formed by conductor bars laid in slots of a sheet steel body. The conductor bars have a central metallic conductor (usually consisting of a plurality of partial conductors made from drawn copper wire with predominantly rectangular cross section). The conductor bars likewise have a predominantly rectangular cross section and are surrounded by an insulation of defined thickness (see, for example, publications DE-A1-198 11 370 or EP-B1-1 319 266). The insulation is frequently constructed by winding a glass/mica tape several times around the conductor, said tape being impregnated with artificial resin in order to remove air pockets and for strengthening.
These days, glass/mica tapes are applied almost exclusively by machine using special winding robots. In doing so, the rolls of tape are moved in a rotating ring along the longitudinal direction of the bar and the tape is wound on in several layers with about 50% overlap in the form of a spiral until the required thickness is reached.
A distinction is made between different winding methods, which are referred to as “parallel winding” and “cross winding”:
Parallel winding: Winding is always carried out in one direction only (see FIG. 2). All tape edges of different tape layers or winding layers lie parallel to one another. The disadvantage here is that when a layer has been completed, the winding ring must be returned “empty”, which means lost time within the manufacturing process.
Cross winding: Here, winding is carried out backwards and forwards in alternate directions (see FIG. 3). As a result, the alignment of the edges of tapes of two successive layers reverses (in a similar way to a bandage on a wound). This is the method of winding used almost exclusively today. A disadvantage of cross winding is that, without considerable effort, it cannot be avoided that at some point in time the crossing points of two tape layers come to lie on an edge of the conductor.